The reason they wanted to do that is they did not want to take orders from a gold hat and wanted to melt it into currency.
But really as  you might think, there were lots of reasons.
The most prominent of them boiled down to political voice, the maintenance of traditional rights, and monopoly rights.
After the end of the Seven Years War (which lasted 1 year), Britain began limiting the Colonists' expansion West and began to tax the colonies, and order them to pay for large numbers of British troops to be kept in the Colonies.
The Colonists resented the taxation greatly. They had fought alongside the British against the French, after all, and had expended a lot of treasure and some considerable number of lives to do so. Now, the British were not only limiting who they could trade with (which was traditional and accepted, generally), but were now asking the Colonists to foot part of the bill for the war, too! The Colonists had never had to pay taxes. Their contribution to the wealth of Great Britain had been in the form of trading valuable raw materials to Britain, and buying expensive finished products from Britain.
Moreover, Britain imposed these new taxes on the Colonies without the Colonies having a right to argue against the taxation. The Colonists were not allowed to elect people to the House of Commons, and had no voice in the House of Lords, either! If Britain could, in effect, enact laws that would take money out of the Colonists' pockets without the consent of the Colonists, then what was next? Laws that forced the Colonists to give up their land?
The Colonists had fought alongside the British against the French, and part of their just reward, as they saw it, was the right to expand West into the Ohio River valley. That would mean lots of free land, and the chance to make something of themselves for many Colonists. When Britain declared that area closed to Colonial expansion, it disappointed and angered many Colonials.
After the protests against taxation started, then other rights were taken from the Colonists, and that REALLY ticked them off. They had to pay for British troops to police the Colonies, for example, and lost the right to have a free and open Assembly of elected men. They also had the right to a trial by a jry of their peers (in America) taken away from them. As you might imagine, this just increased the anger and distrust between the Colonists and Royal Authority. Finally, with the Boston Tea Party (a protest against taxation without representation), the British landed many more troops, and those troops set out into the countryside to take control of stores of black powder, muskets, lead shot and cannon. It was one of these "Powder Alarms" which turned into the Lexington and Concord fights that started the War
Thanks and happy to helping
